In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Superhard materials include, for example, diamond, cubic boron nitride and polycrystalline diamond. Diamonds and cubic boron nitride (“CBN”) have been widely used as abrasives on saws, drills, and other tools that utilize the abrasive to cut, form, or polish other hard materials. Polycrystalline diamond (“PCD”) cutting elements are generally known. A PCD compact is a mass of diamond particles, bonded together to form an integral, tough, high-strength mass. Diamond or CBN particles may be bonded together as a compact in a particle-to-particle self-bonded relationship, optionally with a bonding medium disposed between the particles, such as a catalyzing material used to bond the abrasive particles together. For example, U.S. Pat. Nos. 3,236,615; 3,141,746; and 3,233,988, the disclosures of each of which are herein incorporated by reference in their entirety, describe PCD compacts and methods of forming the same.
An abrasive particle compact may be bonded to a substrate material, such as cemented tungsten carbide. Compacts of this type, i.e., when bonded to a substrate, are sometimes referred to as composite compacts, such as the compacts described in U.S. Pat. Nos. 3,743,489; 3,745,623; and 3,767,371, the disclosures of each of which are herein incorporated by reference in their entirety, or are sometimes referred to as a cutting element or a cutter.
Abrasive compacts and composite compacts have found utility incorporated into drill bits. Drill bits for use in rock drilling, machining of wear resistant materials, and other operations which require high abrasion resistance or wear resistance generally consist of a plurality of abrasive compacts and/or composite compacts affixed to the drill bit or embedded into the body of the drill bit. For example, U.S. Pat. Nos. 4,109,737 and 5,374,854, the disclosures of each of which are herein incorporated by reference in their entirety, describe drill bits with a tungsten carbide substrate having a polycrystalline diamond compact on the outer surface of the cutting element.
Abrasive compacts and composite compacts incorporating superhard materials are used in drilling, mining, and woodworking applications. Abrasive compacts and composite compacts have been designed to provide variously, among other things, abrasion resistance impact strength, and/or advantageous thermal stability. Accordingly, abrasive compacts and composite compacts of all types may be mounted by various means, e.g., by interference fit, by brazing, by direct incorporation into the body of the bit or by other mounting methods, to form drill bits. Drill bits can, for example, include rotary drill bits, roller cone bits, and drag bits.
Drilling and mining operations, in particular, require a cutter system to withstand impacts observed in transitional drilling and drilling through tough formations. In addition, the wash of the drilling and/or cutting operation is very abrasive and contributes to wear of the cutter. As the performance of the superhard material such as PCD increases, so does the need to improve the performance of the substrate supporting the superhard material. For example, underperformance of the substrate relative to the superhard material in regards to wear can result in substrate wear that reduces the integrity of the mounting method and can result in failure of the cutter mounting that is premature relative to the time period in which the superhard material would otherwise fail or be exhausted. Further, cutters are typically rotated during a remounting operation to place a new wear edge into surface and thereby extend the life of the cutter as a whole. Two, three or more rotations may be available depending on cutter size before the cutter as a whole is exhausted. Remounting is usually accomplished by unbrazing and rebrazing the cutter, or by unmounting and remounting the cutter by other methods.
However, if the substrate wears at a rate that is greater than the aggregate of the superhard material over the number of rotations, then support for the superhard material and an attachment area for remounting is not sufficient. This results in the cutter not being used to its maximum lifetime. FIG. 1 is a general schematic cross-section of a cutter 10 showing the superhard material 12 and the substrate 14 and illustrating the general areas of wear 16 that disadvantageously occurs on the substrate 14.